Fix the gem name in README.

Author: kaspth

README.md

@@ -6,15 +6,15 @@ TODO
 
 Add this line to your application's Gemfile:
 
-    gem 'rails-dom-testing'
+    gem 'rails-controller-testing'
 
 And then execute:
 
     $ bundle
 
 Or install it yourself as:
 
-    $ gem install rails-dom-testing
+    $ gem install rails-controller-testing
 
 ## Usage